Smoking rate trends of male 7th and 11th graders in Japan based on repeated, nationwide, cross-sectional surveys every 4 years from 1996 to 2008

Hideyuki Kanda, Yoneatsu Osaki, Yoshitaka Kaneita, Osamu Itani, Maki Ikeda, Takashi Ohida

Department of Environmental and Preventive Health, School of Medicine, Tottori University, Yonago, Japan.
Department of Epidemiology and Public Health, School of Medicine, Ohita University, Ohita, Japan.
Department of Epidemiology and Public Health, School of Medicine, Yokohama City University, Yokohama, Japan;.
Department of Public Health, School of Medicine, Nihon University, Tokyo, Japan.

DOI: 10.4236/health.2013.58168                

Abstract

Backgrounds: Smoking in childhood has become an important public health concern. Previous studies have reported on secular trends in childhood smoking rates and compared with smoking rates at fixed ages. They also described secular trends regarding the prevalence of smoking at fixed ages. The variations in smoking rate of young children and adolescents by follow-up groups have not been studied by follow-up groups at a national level. Objective: We looked at trends and generational impacts on smoking rate by using follow-up groups of male Japanese high school students to quantitatively assess differences in trends, based on multiple nationwide data from the Japanese Youth Tobacco and Drinking Surveys gathered every 4 years between 1996 and 2008. Methods: The surveys were nationwide, cross-sectional random sampling surveys given every 4 years from 1996 to 2008, using the single-stage cluster sampling methodology. The cluster unit of the sampling was school. The survey targeted junior and senior high school students from schools selected through Japan using the National School Directory. Students enrolled in the sampled schools were subjects of the study. Participants were 53,925 high school students from 7th grade to 11th grade in 1996, 2000, 2004 and 2008. We divided the three follow-up groups every 4 years from 1996 to 2004 for male junior high school students in 7th grades, age 13. The end periods were 4 years later when they had become 11th graders, age 17, from 2000 to 2008. Main outcome measures in this study were life time smoking, current smoking within 30 days and daily smoking at 7th or 11th grade and the trend of the smoking rates between 7th to 11th grades. Results: Life time smoking rate, current smoking rate and daily smoking rate in Japanese high school students decreased at 7th grade from 1996 to 2004. They also decreased at 11th grade from 2000 to 2008. However, the slopes differed among their follow-up groups. The increments in their smoking rates from 7th grade to 11th grade in male high school students were smaller in recent follow-up groups both in 2000 and in 2004 than in follow-up groups in 1996. Then, those increments in follow-up groups between in 2000 and in 2004 were similar in lifetime smoking rate and current smoking rate. Conclusions: We have shown that monitoring trends by follow-up group are important in studying smoking for public health. Values of smoking rates from a young age to adolescence by follow-up group should be examined. Values of smoking rate and regular changes in smoking rate are important because smoking rate changes dynamically during adolescence. Not only trends in smoking rates at fixed ages, but also generational impacts should be considered by using follow-up groups to study smoking behaviors among students. We need to continue careful monitoring of follow-up group smoking prevalence. When long-term health promotions are planned or assessed, policy makers need to look at changes in follow-up groups.

Keywords

Smoking Rates; Repeated Cross-Sectional Study; Nationwide Survey; Japan

1. INTRODUCTION

Smoking in childhood has become an important public health concern because early smoking is considered to result in smoking in later life and a higher prevalence of smoking-related disorders [1]. Thus, monitoring changes in smoking rate over time is helpful [1]. Several papers have reported on secular trends in childhood smoking rates, compared smoking rates at fixed ages, and described secular trends regarding the prevalence of smoking, as defined by smoking rate [2-5]. Most of these studies have shown increasing smoking rates and a prevalence of smoking in children.

Smoking rates of young children and adolescents have also been reported [6]. However, most of these data were based on cross-sectional studies. When estimating the rate increment for a follow-up group, the slope may be distorted by cohort effects [7-9]. The shapes of trends of young children and adolescents by studying follow-up groups have not been examined at a national level. The variations in smoking rate of young children and adolescents by follow-up groups have not been studied by follow-up groups at a national level, and no reported study has compared trends among multiple follow-up groups in a nation.

Frequent observations are needed to compare trends in smoking rates among multiple follow-up groups belonging to the same grade in different years. In this study, we looked at trends and generational impacts on smoking rate by using follow-up groups of male Japanese high school students to quantitatively assess differences in trends. We used nationwide data from the Japanese Youth Tobacco and Drinking Surveys, gathered every 4 years between 1996 and 2008.

2. METHODS

2.1. Subjects and Procedure

The surveys were nationwide, cross-sectional random sampling surveys given every 4 years from 1996 to 2008, using the single-stage cluster sampling methodology [10]. Previous studies detailing the Japanese Youth Tobacco and Drinking Surveys have been reported [2,11-13]. The cluster unit of the sampling was schools. The survey targeted junior and senior high school students from schools selected through Japan using the National School Directory. All students enrolled in the sampled schools were subjects of the study.

The number of schools sampled in the 1996 survey was 122 of 11,274 junior high schools (selection rate: 1.1%) and 109 of 5501 senior high schools (2.0%). Respective values for the 2000, 2004 and 2008 surveys were 132 of 11,200 junior (1.2%) and 102 of 5315 senior high schools (1.9%) in the 2000 survey, 131 of 11,060 junior (1.2%) and 109 of 5272 senior high schools (1.9%) in the 2004 survey, and 130 of 10,955 junior (1.2%) and 110 of 5115 senior high schools (2.0%) in the 2008 survey.

We requested the cooperation of the principals of these schools and sent these individuals questionnaires for their respective school’s student population. The teachers were asked to inform the students of the voluntary nature of their participation and to urge them to answer honestly. Anonymous questionnaires and envelopes were handed to the students for completion during school time. Upon completion, the questionnaires were sealed in the envelopes by the students themselves, collected by their teachers, and returned to our researchers unopened. This survey was reviewed and approved by the institutional review board of Nihon University (No. 19-5-0).

2.2. Questionnaire

The questionnaire focused on smoking experience, smoking frequency, and age. Experimenting smokers, current smokers, and daily smokers were defined as those who had tried smoking at least once, those who had smoked at least once during the previous 30 days, and those who had smoked every day during the previous 30 days, respectively.

2.3. Responses

For the 1996 survey, responses were obtained from 80 junior (response rate 65.5%) and 73 senior high schools (67.0%). In 2000, the respective values were 99 (75.0%) and 77 schools (75.5%), and in 2004, there were 92 (70.2%) and 87 schools (79.8%). In 2008, the respective values were 92 (70.8%) and 73 schools (72.7%).

We used data from the 1996-2004 surveys for male junior high school students in 7th grade, age 13. We divided to the three follow-up groups every 4 years from 1996 to 2004. The end periods were 4 years later when they had become 11th graders, age 17, from 2000 to 2008. Table 1 shows a summary of follow-up groups. All group data includes all of the smoking rates from 7th grade to 11th grade. The total sample size of the 1996-2008 surveys was 53,925. We compared smoking rate increments from 7th to 11th grade for 3 follow-up

Table 1. Follow-up groups of male students in this survey, Japan, 1996-2008.

groups as well as each smoking rate in both 7th grade and 11th grade for 3 follow-up groups.

2.4. Statistical Analysis

The percentages in the tables were calculated by a weighting method based on one-stage stratified cluster sampling10. We estimated the mean values of smoking rate by follow-up group. We calculated the change in smoking rate by subtracting the previous smoking rate from the current one, by follow-up group. Data were analyzed using the SPSS ver. 21.0 software (SPSS, Tokyo, Japan).

3. RESULTS

3.1. Trends of Lifetime Smoking Rates

Figure 1 shows the trends of the lifetime smoking rate for the three follow-up groups (1996, 2000 and 2004) of Japanese male students from 7th grade to 11th grade. The lifetime smoking rates decreased at 7th grade from 1996 to 2004 in males. They also decreased at 11th grade from 2000 to 2008. However, the increments in the lifetime smoking rate from 7th grade to 11th grade in high school students were smaller in recent follow-up groups both in 2000 and in 2004 than in follow-up groups in 1996. Then, those increments in follow-up groups between 2000 and 2004 were similar; around +13% in males from 7th grade to 11th grade.

Conflicts of Interest

The authors declare no conflicts of interest.

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